Recently, in order to achieve higher integration levels in semiconductor integrated circuits, the MOS transistors used and other elements have been miniaturized. In general, by miniaturizing MOS transistors, a low-voltage element is obtained with a lowered threshold voltage and gate voltage and a narrow MOS transistor operating voltage range. Hence a step-down power supply circuit is used in order to enable the low-voltage elements in the semiconductor integrated circuit to operate normally. Examples of step-down power supply circuits are given in Japanese Patent Application Laid-open No. 2005-148942 and Japanese Patent Application Laid-open No. H9-330135. A step-down power supply circuit steps down an external power supply voltage to generate a desired step-down voltage, which is supplied to the internal integrated circuit, and in addition controls the step-down voltage based on a reference voltage from an internal reference voltage generation circuit.
However, in the case of large variation in the reference voltage of the reference voltage generation circuit, the step-down voltage is calibrated using a voltage tester or the like connected to the semiconductor integrated circuit and the calibration data is stored in a memory of a calibration circuit. Hence, increased manufacturing costs result. On the other hand, in the case of using the reference voltage generation circuit with small variation of the reference voltage, the power consumption of the reference voltage generation circuit increases because a variation of the reference voltage and a power consumption of the reference voltage generation circuit are in a trade-off relationship in general.